There are two main objectives for the proposed project period: first, techniques and vectors will be developed to extend the utility of the FLP site-specific recombinase as a tool for genetic manipulations; second, this technique will be applied to a mosaic analysis of the genetic factors controlling male fertility. Experiments that are aimed at elucidating how the three classes of male-sterilizing mutations differ in their modes of action will be performed. Of particular interest is the mechanism by which specific types of chromosomal rearrangement cause male sterility. The long term objective is to identify the genes that control and carry out the normal processes underlying this phenomenon, and characterize them in molecular detail. To these ends the following goals have been set: 1. A detailed analysis of the factors that influence the frequency of FLP-mediated recombination between FRTs will be performed. This will provide a solid footing for further work with this system. 2. Methods and vectors to perform site-specific integration of exogenous DNA will be developed. 3. Vectors and screening techniques will be developed to allow the easy recovery of site-specific chromosomal rearrangements. 4. Germline mosaics for three different classes of male-sterilizing mutations -- single gene mutations, Y chromosome fertility factors, and chromosomal rearrangements -- will be produced at different stages of spermatogenesis and compared. The experiments will help to define the mode of action by which each of these classes of mutation sterilizes males. The notion that spermatocytes function nonautonomously will be tested. 5. High-frequency dicentric formation will be employed to analyze the fate of dicentric chromosomes and the cells that carry them. The analysis will encompass cis-acting elements, the fate of dicentric- bearing cells, and the fates of dicentrics in the soma and in the germline. 6. A mutation screen will be performed to identify genes that function autonomously in spermatocytes. The project will provide insight into the genetic control of male fertility and into the cellular consequences of chromosome aberrations and aneuploidy.